Lloyd AJ, Moore PB, Cousins DA, Thompson JM, McAllister VL, Hughes JH, Ferrier IN, Young AH. White matter lesions in euthymic patients with bipolar disorder. Objective: We aimed to quantify both load and regional distributions of hyperintensities on magnetic resonance imaging (MRI) in prospectively verified euthymic bipolar patients and matched controls. Method: Cerebral hyperintensities on T2, proton density and fluid-attenuated inversion recovery (FLAIR) MRI were compared between 48 bipolar and 47 control subjects using semi-quantitative rating scales. Results: Bipolar subjects had more severe frontal deep white matter lesions (DWML). Hyperintensity load was independent of age in bipolar patients but increased with age in controls. Global prevalence and severity of hyperintensities did not differ between groups. Exploratory analysis showed DWML in excess in the left hemisphere in bipolar subjects but not in controls. Conclusion: Findings are consistent with clinical, particularly some neurocognitive, features of bipolar disorder and implicate fronto-subcortical circuits in its neurobiology. They more probably reflect a trait abnormality or illness scar rather than a mood state-dependent finding. Processes other than ageing and vascular factors may underlie their development.